Solution
= Solution
Use the <phasor> convention $v(t)=\operatorname{Re}(\widetilde V e^{i\omega t})$. The <complex impedance> is $Z=\widetilde V/\widetilde I$ in sinusoidal steady state. From $v_R=Ri$, $i_C=C\,dv_C/dt$, and $v_L=L\,di_L/dt$,
$$
\boxed{Z_R=R,\qquad Z_C=\frac1{i\omega C}=-\frac{i}{\omega C},\qquad Z_L=i\omega L.}
$$
For this convention an ideal <inductor> has voltage leading current by $\pi/2$, while an ideal <capacitor> has current leading voltage by $\pi/2$.